Many cold cathode fluorescence lamps and hot cathode fluorescence lamps are used as a light source for back light of a liquid crystal display panel or a lamp for lighting. A very small amount of mercury is enclosed in these lamps, in which light is emitted from a phosphor due to ultraviolet rays generated from the mercury excited by electric discharge, and they are excellent in terms of high brightness and efficient luminescence.
However, a new light source which does not contain mercury is desired from a viewpoint of prevention of environmental pollution. In a proposed fluorescence lamp which does not contain mercury, two or more belt-like electrodes are disposed on the external surface of a glass tube, and high-frequency high-voltage boosted by a boosting transformer is impressed to these electrodes so as to turn on the rare gas fluorescence lamp. As disclosed in Japanese Patent No. 3,149,780, in such a rare gas fluorescence lamp, an initiation assisting portion for assisting initiation of the rare gas fluorescence lamp is formed, by applying, for example, a conductive substance to the interior of a glass tube end portion.
Moreover, in an external electrode type rare gas fluorescence lamp which is turned on by impressing high-frequency high-voltage thereto, as disclosed in Japanese Laid Open Patent No. H06-163008, the lamp voltage waveform impressed to the electrode is not sinusoidal voltage but voltage including steep voltage changes like a rectangle waveform voltage, so that the light emitting efficiency may be improved.
Generally, the brightness of the screen of a liquid crystal display panel equipped with such a rare gas fluorescence lamp can be adjusted according to surrounding brightness, preference of a user, and/or image information, etc. Adjustment of the brightness on the screen is performed by controlling a back light. In general, the back light is controlled by burst light control. Moreover, also in a lighting use, for example, indirect illumination, in order to adjust the brightness matched with the use environment, a wide range of light adjustment is required. In those cases, burst light control is used in general, as in case of the back light. The burst light control is also called duty light control, in which a cycle of lighting and non-lighting is repeated at a frequency of 60 Hz or higher, and the lighting and non-lighting are periodically repeated at a frequency in a range of approximately 60 to 1 KHz so that the ratio of lighting time and non-lighting time is controlled so as to adjust light The light control frequency is selected from a range of about 60-300 Hz in the case of the liquid crystal back light, and about 1 kHz in the case of a lighting use. The frequency is not limited thereto and can be chosen from the range in which man's eyes cannot recognize it.